The present invention relates generally to a hermetic scroll-type compressor and, more particularly, to such a compressor having fixed and orbiting scroll members, wherein a compliance mechanism acts to bias the fixed and orbiting scroll members toward one another for proper mating and sealing therebetween.
A typical scroll compressor comprises two facing scroll members, each having an involute wrap, wherein the respective wraps interfit to define a plurality of closed compression pockets. When one of the scroll members is orbited relative to the other, the pockets decrease in volume as they travel between a radially outer suction port and a radially inner discharge port, thereby conveying and compressing the refrigerant fluid.
It is generally believed that the scroll-type compressor could potentially offer quiet, efficient, and low-maintenance operation in a variety of refrigeration system applications. However, several design problems persist that have prevented the scroll compressor from achieving wide market acceptance and commercial success. For instance, during compressor operation, the pressure of compressed refrigerant at the interface between the scroll members tends to force the scroll members axially apart. Axial separation of the scroll members causes the closed pockets to leak at the interface between the wrap tips of one scroll member and the face surface of the opposite scroll member. Such leakage causes reduced compressor operating efficiency and, in extreme cases, can result in an inability of the compressor to operate.
Leakage between compression pockets of a scroll compressor may also occur at those locations where the wrap walls sealingly contact each other to define the moving compression pockets. Specifically, the pressure of the compressed refrigerant in the compression pockets, together with manufacturing tolerances of the component parts, may cause slight radial separation of the scroll members and result in the aforementioned leakage.
Efforts to counteract the separating forces applied to the scroll members during compressor operation, and thereby minimize the aforementioned leakages, have resulted in the development of several prior art compliance schemes. With respect to axial compliance mechanisms, the scroll members may be preloaded axially toward each other with a force sufficient to resist the dynamic separating force. However, this approach results in high initial frictional forces between the scroll members and/or bearings when the compressor is at rest, thereby causing difficulty during compressor startup. Another prior art approach involves assuring close manufacturing tolerances for component parts and having the separating force borne by a thrust bearing. This approach not only requires an expensive thrust bearing, but also involves high manufacturing costs in maintaining close machining tolerances.
In a compressor having a pressurized, or "high side", housing, discharge pressure may be used on the back side of the fixed or orbiting scroll member to create a force to oppose the separating force. In such an arrangement, it is difficult to control the magnitude of the resulting force and excessive friction and power losses may result. One solution has been to use a combination of gaseous refrigerant at suction pressure and gaseous refrigerant at discharge pressure, and expose them to respective areas on the backside of an axially movable fixed or orbiting scroll member. In such compressor designs, various seal means have been utilized to separate the respective gaseous pressure regions and to compensate for axial movement of the scroll member.
In another type of axial compliance mechanism, an intermediate pressure chamber is provided behind the orbiting scroll member, whereby the intermediate pressure creates an upward force to oppose the separating force. Such a design recognizes the fact that only suction pressure behind the orbiting scroll member is insufficient to oppose the separating force, while discharge pressure behind the orbiting scroll member results in too great an upward force and may cause rapid wear of the scroll wraps and faces. However, establishing an intermediate pressure between suction pressure and discharge pressure requires that an intentional leak be introduced between an intermediate pressure pocket and a discharge pressure region. Such a leak results in less efficient operating conditions for the compressor.
The present invention is directed to overcoming the aforementioned problems associated with scroll-type compressors, wherein it is desired to provide axial forces on the mating scroll members to facilitate sealing and prevent leakage.